This invention is directed to structurally-modified water-soluble polymers prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization and adding at least one modifier after at least 30% polymerization of the monomers has occurred, and to the use of the polymers as flocculants.
Water-soluble polymeric flocculants are commonly used for clarifying suspensions of organic matter of a proteinaceous or cellulosic nature such as those found in sewage and industrial plant treatment effluents or in paper mills.
These suspended materials are hydrophilic in nature and often have specific gravities quite close to the aqueous liquors in which they are suspended, and differ in a marked way with more hydrophobic mineral suspensions in that they are frequently much more difficult to flocculate economically with chemical reagents prior to a physical dewatering step such as filtration, flotation, sedimentation or dewatering. These difficulties are particularly noticeable when higher proportions of suspended matter are present, commonly involving concentrations of 0.5 percent by weight and upwards where the suspensions take on a paste-like consistency and are commonly described as sludges.
It is well known that the clarification or dewatering of sewage and industrial sludges and similar organic suspensions may be aided by chemical reagents, added in order to induce a state of coagulation or flocculation which facilitates the process of solid/liquid or liquid/liquid separation from water. For this purpose, lime or salts of iron or aluminum have been utilized. More recently synthetic polyelectrolytes, particularly certain cationic and anionic copolymers of acrylamide, have been found to be of interest.
While strictly mechanical means have been used to effect solids/liquid separation, modem methods often rely on mechanical separation techniques that are augmented by synthetic and natural polymeric materials to accelerate the rate at which solids can be removed from water. These processes include the treatment of raw water with cationic coagulant polymers that settle suspended inorganic particulates and make the water usable for industrial or municipal purposes. Other examples of these processes include the removal of colored soluble species from paper mill effluent wastes and the use of polymeric flocculants for the treatment of industrial water, as sludge conditioners for the treatment of municipal water systems, as retention and drainage aids in the manufacture of paper, as chemicals for recovering useful and valuable substances from white water in the papermaking process and in emulsion breaking.
A benchmark test for evaluating the effectiveness of a flocculant is the so-called drainage test in which the polymer is added to sludge and mixed so that the polymer flocculates the sludge. The mixture is then poured through a belt filter press cloth and the rate at which water drains is taken as a measure of polymer performance.
Regarding the mechanism of separation processes, particles in nature have either a cationic or anionic charge. Accordingly, these particles often are removed by a water-soluble coagulant or flocculant polymer having a charge opposite to that of the particles. This is referred to as a polyelectrolyte enhanced solids/liquid separation process, wherein a water-soluble or dispersible ionically charged polymer is added to neutralize the charged particles or emulsion droplets to be separated. The dosage of these polymers is critical to the performance of the process. Too little ionically charged polymer, and the suspended particles will not be charge neutralized and will thus still repel each other. Too much polymer, and the polymer will be wasted, or worse, present a problem in and of itself.
Notwithstanding the variety of commercially available polymers that have been found to be capable of flocculating or coagulating sludges, there are various circumstances which tend to limit the usefulness of these reagents. While for certain sludges economical treatments with these known reagents are feasible, more often sludges require very high and cost-ineffective dosages of reagents for successful treatment. Moreover, variations often occur in sludge from any one source. For example, variations in the supply of material to the waste water/sludge/paper furnish process water and/or in the oxidizing conditions that may be involved in the production of these waters lead to a variety of particle types which must be removed. Furthermore, it is not uncommon to encounter sludges that are, for some reason, not amenable to flocculation by any of the known polymeric flocculating agents.
Therefore, there is a need for an improved family of polymers that provide better drainage at lower doses in sludge dewatering. Likewise, there is a continuing need for treatments to increase the efficiency of pulp and paper manufacture.
EP 202,780 discloses particulate cross-linked copolymers of acrylamide with at least 5 mole percent dialkylaminoalkyl acrylate for use as flocculants in high-shear applications.
The addition of a cross-linking agent both at the beginning, and during the polymerization process under conditions such that its availability for reaction is substantially constant throughout the process is disclosed in U.S. Pat. No. 4,950,725.
EP 374,458 discloses water-soluble branched high molecular weight cationic flocculants formed from monomers polymerized in the presence of chain transfer agents such as isopropanol and branching agents such as methylene bisacrylamide, in which the chain transfer agent is added to prevent cross linking. Cross linking can render the polymer insoluble in water.
Addition of chain transfer agent at the conclusion of polymerization of a DADMAC/acrylamide copolymer to produce a linear higher molecular weight copolymer is disclosed in EP 363,024.
U.S. Pat. No. 4,913,775 discloses use of substantially linear cationic polymers such as acrylamide/dimethylaminoethyl acrylate methyl chloride quaternary salt copolymers and bentonite as additives in pulp or paper manufacture.
U.S. Pat. No. 5,393,381 discloses use of a branched cationic polyacrylamide powder such as an acrylamide/dimethylaminoethyl acrylate quaternary salt copolymer and bentonite for paper or cardboard manufacture.
We have discovered that the late stage addition to a polymerization reaction of a structural modifier as described herein results in formation of a more effective, structurally-modified flocculant. When the structural modifier is a chain-transfer agent, the resulting water-soluble polymers typically have a faster rate of solubilization, higher reduced specific viscosities and are more active than unmodified analogs. This is applicable to cationic, anionic, or nonionic polymers, synthesized using water-in-oil emulsion, dispersion, or gel polymerization techniques.
Accordingly, in its principal aspect, this invention is directed to a water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
As used herein, the following abbreviations and terms shall have the following meanings.
xe2x80x9cAcAmxe2x80x9d for acrylamide.
xe2x80x9cDADMACxe2x80x9d for diallyldimethylammonium chloride.
xe2x80x9cDMAEAxe2x80x9d for dimethylaminoethyl acrylate.
xe2x80x9cDMAEMxe2x80x9d for dimethylaminoethyl methacrylate.
xe2x80x9cDMAEA. BCQxe2x80x9d for dime thylaminoethyl acrylate, benzyl chloride quaternary salt.
xe2x80x9cDMAEA. MCQxe2x80x9d for dimethylaminoethyl acrylate, methyl chloride quaternary salt.
xe2x80x9cEDTA. 4Na+xe2x80x9d for ethylenediaminetetraacetic acid, tetrasodium salt.
xe2x80x9cAlfonic(copyright) 1412-60xe2x80x9d is a ethoxylated linear alcohol (60% ethylene oxide), available from Vista Chemical Co., Houston, Tex.
xe2x80x9cSpan 80xe2x80x9d for sorbitan monooleate available from ICI Specialty Chemicals, Wilmington, Del.
xe2x80x9cTriton(copyright) N-101 xe2x80x9d for nonylphenoxy polyethoxy ethanol, available from Rohm and Haas Co., Philadelphia, Pa.
xe2x80x9cTween 61 xe2x80x9d for POE (4) sorbitan monostearate, available from ICI Specialty Chemicals, Wilmington, Del.
xe2x80x9cAIBNxe2x80x9d for 2,2xe2x80x2-azobis(isobutyronitrile), available from E. I. duPont Nemours and Co. Inc.; Wilmington, Del.
xe2x80x9cAIVNxe2x80x9d for 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile), available from E. I. duPont Nemours and Co. Inc.; Wilmington, Del.
xe2x80x9cPOExe2x80x9d for polyoxyethylene.
xe2x80x9cRSVxe2x80x9d stands for Reduced Specific Viscosity. Within a series of polymer homologs which are substantially linear and well solvated, xe2x80x9creduced specific viscosity (RSV)xe2x80x9d measurements for dilute polymer solutions are an indication of polymer chain length and average molecular weight according to Paul J. Flory, in xe2x80x9cPrinciples of Polymer Chemistryxe2x80x9d, Cornell University Press, Ithaca, N.Y., (copyright) 1953, Chapter VII, xe2x80x9cDetermination of Molecular Weightsxe2x80x9d, pp. 266-316. The RSV is measured at a given polymer concentration and temperature and calculated as follows:       RSV    =                  [                              (                          η              /                              η                o                                      )                    -          1                ]            c                                    η          =                      viscosity of polymer solution                                                                    η            o                    =                      viscosity of solvent at the same temperature                                                        c          =                      concentration of polymer in solution.                              
The units of concentration xe2x80x9ccxe2x80x9d are (grams/100 ml or g/deciliter). Therefore, the units of RSV are dl/g. In this patent application, a 1.0 molar sodium nitrate solution is used for measuring RSV, unless specified. The polymer concentration in this solvent is 0.045 g/dl. The RSV is measured at 30xc2x0 C. The viscosities xcex7 and xcex7o are measured using a Cannon Ubbelohde semimicro dilution viscometer, size 75. The viscometer is mounted in a perfectly vertical position in a constant temperature bath adjusted to 30xc2x10.02xc2x0 C. The error inherent in the calculation of RSV is about 2 dl/grams. When two polymer homologs within a series have similar RSV""s that is an indication that they have similar molecular weights.
xe2x80x9cIVxe2x80x9d stands for intrinsic viscosity, which is RSV extrapolated to the limit of infinite dilution, infinite dilution being when the concentration of polymer is equal to zero.
xe2x80x9cBased on formulaxe2x80x9d means the amount of reagent added based on the total formula weight.
xe2x80x9cBased on polymer activexe2x80x9d and xe2x80x9cbased on monomerxe2x80x9d mean the amount of a reagent added based on the level of vinylic monomer in the formula, or the level of polymer formed after polymerization, assuming 100% conversion.
xe2x80x9cRaw waterxe2x80x9d means water from natural geographical sources including rivers, lakes, well water, rain water, and the like.
xe2x80x9cProcess waterxe2x80x9d means water used in a process such as a manufacturing process (paper machine), steel production, chemical production processes, refinery processes, food production processes (i.e., sugar process), and the like.
xe2x80x9cWaste waterxe2x80x9d means water from a manufacturing process, municipal waste or other waters which are required to be treated prior to discharge to a receiving stream, lake or other water way.
xe2x80x9cPapermaking processxe2x80x9d means a method of making paper products from pulp comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet and drying the sheet. The steps of forming the papermaking furnish, draining and drying may be carried out in any conventional manner generally known to those skilled in the art. Conventional coagulants, conventional flocculants, microparticles, alum, cationic starch or a combination thereof may be utilized as adjuncts with the structurally-modified water-soluble polymer of this invention, though it must be emphasized that no adjunct is required for effective retention and drainage activity.
xe2x80x9cMonomerxe2x80x9d means a polymerizable allylic, vinylic or acrylic compound. The monomer may be anionic, cationic or nonionic. Vinyl monomers are preferred, acrylic monomers are more preferred.

Representative non-ionic, water-soluble monomers include acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, N-vinylformamide, N-vinylmethylacetamide, N-vinyl pyrrolidone, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, N-t-butylacrylamide, N-methylolacrylamide, and the like.
Representative anionic monomers include acrylic acid, and it""s salts, including, but not limited to sodium acrylate, and ammonium acrylate, methacrylic acid, and it""s salts, including, but not limited to sodium methacrylate, and ammonium methacrylate, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), the sodium salt of AMPS, sodium vinyl sulfonate, styrene sulfonate, maleic acid, and it""s salts, including, but not limited to the sodium salt, and ammonium salt, sulfonate itaconate, sulfopropyl acrylate or methacrylate or other water-soluble forms of these or other polymerisable carboxylic or sulphonic acids. Sulfomethylated acrylamide, allyl sulfonate, sodium vinyl sulfonate, itaconic acid, acrylamidomethylbutanoic acid, fumaric acid, vinylphosphonic acid, vinylsulfonic acid, allylphosphonic acid, sulfomethyalted acryamide, phosphonomethylated acrylamide, and the like.
Representative cationic monomers include dialkylaminoalkyl acrylates and methacrylates and their quaternary or acid salts, including, but not limited to, dimethylaminoethyl acrylate methyl chloride quaternary salt, dimethylaminoethyl acrylate methyl sulfate quaternary salt, dimethyaminoethyl acrylate benzyl chloride quaternary salt, dimethylaminoethyl acrylate sulfuric acid salt, dimethylaminoethyl acrylate hydrochloric acid salt, dimethylaminoethyl methacrylate methyl chloride quaternary salt, dimethylaminoethyl methacrylate methyl sulfate quaternary salt, dimethylaminoethyl methacrylate benzyl chloride quaternary salt, dimethylaminoethyl methacrylate sulfuric acid salt, dimethylaminoethyl methacrylate hydrochloric acid salt, dialkylaminoalkylacrylamides or methacrylamides and their quaternary or acid salts such as acrylamidopropyltrimethylammonium chloride, dimethylaminopropyl acrylamide methyl sulfate quaternary salt, dimethylaminopropyl acrylamide sulfuric acid salt, dimethylaminopropyl acrylamide hydrochloric acid salt, methacrylamidopropyltrimethylammonium chloride, dimethylaminopropyl methacrylamide methyl sulfate quaternary salt, dimethylaminopropyl methacrylamide sulfuric acid salt, dimethylaminopropyl methacrylamide hydrochloric acid salt, diethylaminoethylacrylate, diethylaminoethylmethacrylate, diallyldiethylammonium chloride and diallyldimethyl ammonium chloride. Alkyl groups are generally C1-4 alkyl.
xe2x80x9cStructural modifierxe2x80x9d means an agent that is added to the aqueous polymer solution to control the polymer structure and solubility characteristics. The structural modifier is selected from the group consisting of cross-linking agents and chain transfer agents.
xe2x80x9cChain transfer agentxe2x80x9d means any molecule, used in free-radical polymerization, which will react with a polymer radical forming a dead polymer and a new radical. In particular, adding a chain transfer agent to a polymerizing mixture results in a chain-breaking and a concommitant decrease in the size of the polymerizing chain. Thus, adding a chain transfer agent limits the molecular weight of the polymer being prepared. Representative chain transfer agents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, and glycerol, and the like, sulfur compounds such as alkylthiols, thioureas, sulfites, and disulfides, carboxylic acids such as formic and malic acid, and their salts and phosphites such as sodium hypophosphite, and combinations thereof. See Berger et al., xe2x80x9cTransfer Constants to Monomer, Polymer, Catalyst, Solvent, and Additive in Free Radical Polymerization,xe2x80x9d Section II, pp. 81-151, in xe2x80x9cPolymer Handbook,xe2x80x9d edited by J. Brandrup and E. H. Immergut, 3 d edition, John Wiley and Sons, New York (1989) and George Odian, Principles of Polymerization, second edition, John Wiley and Sons, New York (1981). A preferred alcohol is 2-propanol. Preferred sulfur compounds include ethanethiol, thiourea, and sodium bisulfite. Preferred carboxylic acids include formic acid and its salts. More preferred chain-transfer agents are sodium hypophosphite and sodium formate.
xe2x80x9cCross-linking agentxe2x80x9d or xe2x80x9cbranching agentxe2x80x9d means a multifunctional monomer that when added to polymerizing monomer or monomers results in xe2x80x9ccross-linkedxe2x80x9d polymers in which a branch or branches from one polymer molecule become attached to other polymer molecules. Preferred cross-linkers are polyethylenically unsaturated monomers. Representative preferred cross-linking agents include N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, triallylamine, triallyl ammonium salts, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, triethylene glycol dimethylacrylate, polyethylene glycol dimethacrylate, N-vinylacrylamide, N-methylallylacrylamide, glycidyl acrylate, acrolein, glyoxal and vinyltrialkoxysilanes such as vinyltrimethoxysilane (VTMS), vinyltriethoxysilane, vinyltris(xcex2-methoxyethoxy)silane, vinyltriacetoxysilane, allyltrimethoxysilane, allyltriacetoxysilane, vinylmethyldimethoxysilane, vinyldimethoxyethoxysilane, vinylmethyldiacetoxysilane, vinyldimethylacetoxysilane, vinylisobutyldimethoxysilane, vinyltriisopropoxysilane, vinyltri-n-butoxysilane, vinyltrisecbutoxysilane, vinyltrihexyloxysilane, vinylmethoxydihexyloxysilane, vinyldimethoxyoctyloxysilane, vinylmethoxydioctyloxysilane, vinyltrioctyloxysilane, vinylmethoxydilauryloxysilane, vinyldimethoxylauryloxysilane, vinylmethoxydioleyoxysilane, and vinyldimethoxyoleyloxysilane. A more preferred vinylalkoxysilane monomer is vinyltrimethoxysilane.
The water-soluble modified polymers prepared as describe herein may be cationic, anionic or non-ionic. They may be emulsion polymers, dispersion polymers, or gel polymers.
xe2x80x9cEmulsion polymerxe2x80x9d and xe2x80x9clatex polymerxe2x80x9d mean a water-in-oil polymer emulsion comprising a cationic, anionic or nonionic polymer according to this invention in the aqueous phase, a hydrocarbon oil for the oil phase and a water-in-oil emulsifying agent. Inverse emulsion polymers are hydrocarbon continuous with the water-soluble polymers dispersed within the hydrocarbon matrix. The inverse emulsion polymers are then xe2x80x9cinvertedxe2x80x9d or activated for use by releasing the polymer from the particles using shear, dilution, and, generally, another surfactant. See U.S. Pat. No. 3,734,873, incorporated herein by reference. Representative preparations of high molecular weight inverse emulsion polymers are described U.S. Pat. Nos. 2,982,749;3,284,393; and 3,734,873. See also, xe2x80x9cMechanism, Kinetics and Modeling of the Inverse-Microsuspension Homopolymerization of Acrylamide,xe2x80x9d Hunkeler, et al., Polymer (1989), 30(1), 127-42; and xe2x80x9cMechanism, Kinetics and Modeling of Inverse-Microsuspension Polymerization: 2. Copolymerization of Acrylamide with Quaternary Ammonium Cationic Monomers,xe2x80x9d Hunkeler et al., Polymer (1991), 32(14), 2626-40.
The aqueous phase is prepared by mixing together in water one or more water-soluble monomers, and any polymerization additives such as inorganic salts, chelants, pH buffers, and the like.
The oil phase is prepared by mixing together an inert hydrocarbon liquid with one or more oil soluble surfactants. The surfactant mixture should have a low HLB, to ensure the formation of an oil continuous emulsion. Appropriate surfactants for water-in-oil emulsion polymerizations, which are commercially available, are compiled in the North American Edition of McCutcheon""s Emulsifiers and Detergents. The oil phase may need to be heated to ensure the formation of a homogeneous oil solution.
The oil phase is then charged into a reactor equipped with a mixer, a thermocouple, a nitrogen purge tube, and a condenser. The aqueous phase is added to the reactor containing the oil phase with vigorous stirring to form an emulsion. The resulting emulsion is heated to the desired temperature, purged with nitrogen, and a free-radical initiator is added. The reaction mixture is stirred for several hours under a nitrogen atmosphere at the desired temperature. Upon completion of the reaction, the water-in-oil emulsion polymer is cooled to room temperature, where any desired post-polymerization additives, such as antioxidants, or a high HLB surfactant (as described in U.S. Pat. No. 3,734,873) may be added.
The resulting emulsion polymer is a free-flowing liquid. An aqueous solution of the waterin-oil emulsion polymer can be generated by adding a desired amount of the emulsion polymer to water with vigorous mixing in the presence of a high-HLB surfactant (as described in U.S. Pat. No. 3,734,873).
xe2x80x9cDispersion polymerxe2x80x9d means a dispersion of fine particles of polymer in an aqueous salt solution which is prepared by polymerizing monomers with stirring in an aqueous salt solution in which the resulting polymer is insoluble. See U.S. Pat. Nos. 5,708,071; 4,929,655; 5,006,590; 5,597,859; 5,597,858 and European Patent nos. 657,478 and 630,909.
In a typical procedure for preparing a dispersion polymer, an aqueous solution containing one or more inorganic or hydrophobic salts, one or more water-soluble monomers, any polymerization additives such as processing aids, chelants, pH buffers and a water-soluble stabilizer polymer is charged to a reactor equipped with a mixer, a thermocouple, a nitrogen purging tube, and a water condenser. The monomer solution is mixed vigorously, heated to the desired temperature, and then a water-soluble initiator is added. The solution is purged with nitrogen while maintaining temperature and mixing for several hours. After this time, the mixture is cooled to room temperature, and any post-polymerization additives are charged to the reactor. Water continuous dispersions of watersoluble polymers are free flowing liquids with product viscosities generally 100-10,000 cP, measured at low shear.
In a typical procedure for preparing gel polymers, an aqueous solution containing one or more water-soluble monomers and any additional polymerization additives such as chelants, pH buffers, and the like, is prepared. This mixture is charged to a reactor equipped with a mixer, a thermocouple, a nitrogen purging tube and a water condenser. The solution is mixed vigorously, heated to the desired temperature, and then one or more water-soluble free radical polymerization initiators are added. The solution is purged with nitrogen while maintaining temperature and mixing for several hours. Typically, the viscosity of the solution increases during this period. After the polymerization is complete, the reactor contents are cooled to room temperature and then transferred to storage. Gel polymer viscosities vary widely, and are dependent upon the concentration and molecular weight of the active polymer component.
The polymerization reactions described herein are initiated by any means which results in generation of a suitable free-radical. Thermally derived radicals, in which the radical species results from thermal, homolytic dissociation of an azo, peroxide, hydroperoxide and perester compound are preferred. Especially preferred initiators are azo compounds including 2,2xe2x80x2-azobis(2 amidinopropane) dihydrochloride, 2,2xe2x80x2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2xe2x80x2-azobis(isobutyronitrile) (AIBN), 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile) (AIVN), and the like.
The polymerization conditions utilized herein are selected such that the resulting water-soluble structurally-modified polymer has a molecular weight of 2 million to 30 million and an intrinsic viscosity above 1, more preferably above 6 and still more preferably 15 to 30 dl/g. The reduced specific viscosity of the water-soluble structurally-modified polymer is generally above 3, preferably above 12 and frequently above 24 dl/g.
The structural modifiers are added to the reaction mixture after the start of polymerization of the monomers and prior to completion of polymerization of the monomers. They may be added all at once as a single treatment, or in portions. The level of modifier added to the aqueous polymer solution depends on the efficiency of the structural modifier, the polymer concentration, and the degree of polymerization at which it is added.
The degree of polymerization of monomers is determined by the change in the reaction density for water-in-oil emulsion polymerization, calorimeterically by measuring the heat of reaction, by quantitative infrared spectroscopy, or chromatographically, by measuring the level of unreacted monomer.
When a chain-transfer agent is the structural modifying agent, the chain-transfer agent may be added all at once as a single treatment, in portions, or in a manner such that the rate of addition parallels polymer conversion. In one embodiment, addition may be as a single treatment added after about 30%, preferably after about 50% polymerization of the monomers. The level of chain-transfer agent added is generally between from about 1 to about 30,000 ppm, preferably from about 25 to about 10,000 ppm and more preferably from about 50 to about 2,000 ppm based on monomer. When the chain-transfer agent is sodium hypophosphite, the level added is generally from about 2 to about 2000 ppm, preferably from about 100 to about 1000 ppm.
When the structural modifier is a cross-linking agent, the cross-linking agent is added after about 30%, preferably after about 50% polymerization of the monomers. The level of cross-linking agent is generally from about 0.1 to about 500 ppm, preferably from about 1 to about 50 ppm based on monomer. When the cross-linking agent is methylenebisacrylamide, the level is generally from about 0.5 to about 50 ppm, preferably from about 1 to about 10 ppm based on monomer.
When the cross-linker is a vinyltrialkoxysilane, the level of cross-linker is generally from about 0.1 to about 30,000 ppm, preferably from about 0.5 to about 15,000 ppm, more preferably from about 1 to about 3,000 ppm based on monomer. The vinyltrialkoxysilane may be added all at once as a single treatment, or in portions after the polymerization of the monomers has started, preferably after about 30 percent of the monomers have polymerized.
When the structural modifier is a combination of a cross-linker and a chain transfer agent, the amounts of each may vary widely based on the chain-transfer constant xe2x80x9cefficiencyxe2x80x9d of the chain-transfer agent, the multiplicity and xe2x80x9cefficiencyxe2x80x9d of the cross-linking agent, and the point during the polymerization where it is added. For example from about 1,000 to about 5,000 ppm (based on monomer) of a moderate chain transfer agent such as isopropyl alcohol may be suitable while much lower amounts, typically from about 100 to about 500 ppm, of more effective chain transfer agents such as mercaptoethanol are useful. Representative combinations of cross-linkers and chain transfer agents contain from about 1 to about 30,000 ppm, preferably from about 25 to about 10,000 and more preferably from about 300 to about 1500 ppm (based on monomer) of chain transfer agent and from about 1 to about 500, preferably from about 2 to about 100 and more preferably from about 5 to about 50 ppm (based on monomer) of cross-linker. A preferred combination of cross-linker and chain transfer agent is methylenebisacrylamide and formic acid and its salts, preferably sodium formate.
Where the structural modifier is a cross-linking agent, polymers formed by the addition of a cross-linking agent to the polymerization generally between 30% and 99% conversion, preferably between 50 and 90% conversion, and frequently between 65 and 85% conversion, are more active than the unmodified polymers which are substantially linear, cross-linked, water-insoluble particles disclosed in U.S. Pat. No. 4,950,725 and EP 202,780 and the highly branched, water-soluble polymers disclosed in U.S. Pat. No. 5,945,494.
The polymers modified with a cross-linking agent after the start of polymerization differ from the particulate polymer flocculants disclosed in U.S. Pat. No. 4,950,725 and EP 202,780 that are swellable, but, insoluble in water. These particles are formed either through the addition of a watersoluble cross-linking agent, or a mixture of different cross-linking reagents with different reactivities, usually polyethylenically unsaturated monomers at the front-end, or alternatively both at the beginning of the process and at or near the end of the process such that the availability of the cross-linker is substantially constant throughout the reaction or by cross-linking preformed watersoluble polymers. Polymers modified with a cross-linking agent as described herein are not particulate in aqueous solution.
The polymers of this invention also differ from polymers disclosed in U.S. Pat. No. 5,945,494, which are water-soluble, highly branched species. Essential to the formation of these polymers is the inclusion of a molecular weight modifying, or chain-transfer agent in combination with high levels of a branching agent (4 to 80 ppm, based on initial molar content) to form highly-branched, watersoluble polymers. As stated in U.S. Pat. No. 5,945,494 column 5, lines 35-38, in the absence of a chaintransfer agent, the incorporation of even extremely small amounts of branching agent, e.g. 5 parts per million may cause crosslinking, rendering the polymer insoluble in water. The combination of a branching agent and a molecular weight modifying agent included in the aqueous monomer solution at the start of reaction as disclosed in U.S. Pat. No. 5,945,494, will yield highly branched polymers with polymer chains of limited molecular weight.
It is believed that polymers modified with a cross-linking agent after the start of polymerization described herein contain a mixture of linear high molecular weight polymer formed during the initial part of the reaction, and long-chain branched polymer formed during the latter part of the reaction. For aqueous solutions made-up from polymers modified using late addition of a cross-linking agent, it is possible that water-soluble, non-particulate, aggregates of several entangled polymer chains exist. Macromolecular entanglements have been proposed for high molecular weight polymers, formed by free-radical polymerization methods (Gardner, et. al., J. Applied Polymer Science, 22 881-882, (1978); A. Wan, Polymer Preprints, Am. Chem. Soc., Division of Polymer Chemistry, 37(2), 655, (1996).
In a preferred aspect of this invention, the structurally-modified water-soluble polymer is selected from the group consisting of emulsion polymers, dispersion polymers and gel polymers.
In another preferred aspect, the monomers are selected from acrylamide or methacrylamide and one or more monomers selected from the group consisting of diallyldimethylammonium chloride, dimethylaminoethyl acrylate methyl chloride quaternary salt, acrylamidopropyltrimethylammonium chloride, dimethylaminoethyl methacrylate methyl chloride quaternary salt, methacrylamidopropyltrimethylammonium chloride, acrylic acid, sodium acrylate, ammonium acrylate, methacrylic acid, sodium methacrylate, and ammonium methacrylate.
In another preferred aspect, the structural modifier is selected from the group consisting of cross-linking agents, chain transfer agents and mixtures thereof.
In another preferred aspect, the chain transfer agents are selected from the group consisting of alcohols, sulfur compounds, carboxylic acids or salts thereof, phosphites, and combinations thereof.
In another preferred aspect, the chain transfer agents are selected from sodium formate and sodium hypophosphite.
In another preferred aspect, the cross-linking agent is selected from the group consisting of N,N-methylenebisacrylamide, N,N-methylenebismethacrylamide, triallylamine, triallyl ammonium salts, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, N-vinyl acrylamide, N-methyl allylacrylamide, vinyltrimethoxysilane, and combinations thereof.
In another preferred aspect, the cross-linking agent is vinyltrimethoxysilane.
In another preferred aspect, the cross-linking agent is methylenebisacrylamide.
In another preferred aspect, the monomers are acrylamide and dimethylaminoethylacrylate benzyl chloride quaternary salt and the structural modifier is vinyltrimethoxysilane.
In another preferred aspect, the monomers are acrylamide and diallyldimethylammonium chloride and the structural modifier is vinyltrimethoxysilane.
In another preferred aspect, the monomers are acrylamide and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is methylenebisacrylamide.
In another preferred aspect, the monomers are acrylamide and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is sodium formate.
In another preferred aspect, the monomers are acrylamide and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is sodium hypophosphite.
In another preferred aspect, the monomers are acrylamide and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is a combination of sodium formate and methylenebisacrylamide.
In another preferred aspect, the monomers are acrylamide, dimethylaminoethylacrylate benzyl chloride quaternary salt and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is methylenebisacrylamide.
In another preferred aspect, the monomers are acrylamide, dimethylaminoethylacrylate benzyl chloride quaternary salt and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is sodium formate.
In another preferred aspect, the monomers are acrylamide, dimethylaminoethylacrylate benzyl chloride quaternary salt and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier isa combination of methylenebisacrylamide and sodium formate.
In another preferred aspect, the monomers are acrylamide, dimethylaminoethylacrylate benzyl chloride quaternary salt and dimethylaminoethylacrylate methyl chloride quaternary salt and the structural modifier is vinyltrimethoxysilane.
In another preferred aspect, the monomers are acrylamide and acrylic acid or a salt thereof and the structural modifier is sodium hypophosphite.
In another aspect, this invention is directed to a method of preparing a structurally-modified water-soluble polymer comprising initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
In another aspect, this invention is directed to a method of flocculating an aqueous suspension of organic matter comprising adding to the suspension an effective flocculating amount of the structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
In another aspect, this invention is directed to a method of clarifying waste water comprising adding to the waste water an effective flocculating amount of a structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
The effective flocculating amount of the structurally-modified water-soluble polymer depends on the characteristics of the water being treated and can be readily determined by one of ordinary skill in the art. Polymer should be dosed at a sufficient level to cause flocculation of the dispersed material and cause improved settling. Typical dosages are from about 10 to 1,000 ppm, preferably from about 15 to about 400 ppm and more preferably from about 20 to about 200 ppm based on polymer actives.
In another aspect, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish an effective amount of a structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
The effective amount of the structurally-modified water-soluble polymer depends on the characteristics of the particular papermaking furnish and can be readily determined by one of ordinary skill in the papermaking art. Typical dosages are from about 0.01 to about 6, preferably from about 0.1 to about 4 and more preferably from about 0.1 to about 2 pounds polymer actives/ton solids in the furnish.
The structurally-modified water-soluble polymer of this invention may also be used in combination with a coagulant as part of a dual polymer treatment program. The retention and drainage properties of the furnish may also be improved by addition of a microparticle is described in U.S. Pat. Nos. 4,753,710 and 4,913,775 incorporated herein by reference.
xe2x80x9cMicroparticlesxe2x80x9d means highly charged materials that improve flocculation when used together with natural and synthetic macromolecules. Microparticles are used in combination with other wet end additives to improve retention and drainage on the paper machine. Microparticles encompass a broad set of chemistries including polysilicate microgel, structured colloidal silicas, colloidal alumina, polymers including copolymers of acrylic acid and acrylamide and and naphthalene sulfonate/formaldehyde condensate polymers, bentonite and mineral clays such as montmorillonite, saponite and smectite types and colloidal silica in its many forms including modified colloidal silicic acids such as those described in PCT/US98/19339.
Representative copolymers of acrylic acid and acrylamide usefil as microparticles include Nalco(copyright) 8677 PLUS, available from Nalco Chemical Company, Naperville, Ill., USA. Other copolymers of acrylic acid and acrylamide are described in U.S. Pat. No. 5,098,520, incorporated herein by reference.
xe2x80x9cBentonitesxe2x80x9d include any of the materials commercially referred to as bentonites or as bentonite-type clays, i.e., anionic swelling clays such as sepialite, attapulgite and montmorillonite. In addition, the bentonites described in U.S. Pat. No. 4,305,781 are suitable. A preferred bentonite is a hydrated suspension of powdered bentonite in water. Powdered bentonite is available as Nalbrite(trademark), from Nalco Chemical Company.
Representative dispersed silicas have an average particle size of from about 1 to about 100 nanometers (nm), preferably from about 2 to about 25 nm, and more preferably from about 2 to about 15 nm. This dispersed silica, may be in the form of colloidal, silicic acid, silica sols, fumed silica, agglomerated silicic acid, silica gels, precipitated silicas, and all materials described in Patent Cooperation Treaty Patent Application No. PCT/US98/19339, so long as the particle size or ultimate particle size is within the above ranges. Dispersed colloidal silica in water with a typical particle size of 4 nm is available as Nalco(copyright) 8671, from Nalco Chemical Company. Another type of inorganic colloid used as a microparticle is a borosilicate in water; available as Nalco(copyright) 8692, from Nalco Chemical Company. Other types of colloidal silica and modified colloidal silicas are commercially available from E.I. DuPont de Nemours and Co., Wilmington, Del. under the tradename Ludox(copyright) from Akzo Nobel, Surte, Sweden (BMA or NP Series), from Vinings Industries Inc., Atlanta, Ga. and from Nissan Chemical Industries, Ltd., Tokyo, Japan.
Representative naphthalene sulfonate/formaldehyde condensate polymers include Nalco(copyright) 8678 from Nalco Chemical Company.
The amount of microparticle added is from about 0.05 to about 10, preferably from about 0.1 to about 9 and more preferably about 0.2 to about 6 pounds microparticle/ton.
xe2x80x9cPounds microparticle/tonxe2x80x9d means pounds of actual microparticle per 2000 pounds of solids present in slurry. The abbreviation for pounds of actual microparticle per 2000 pounds of solids present in slurry is xe2x80x9clbs microparticle/tonxe2x80x9d.
The microparticle is added to the papermaking funish either before or after the structurally-modified polymer is added to the furnish. The choice of whether to add the microparticle before or after the polymer can be made by a person of ordinary skill in the art based on the requirements and specifications of the papermaking furnish.
Optionally, a coagulant is added to the furnish prior to the addition of the structurally-modified water-soluble polymer. Preferred coagulants are water-soluble cationic polymers such as epichlorohydrin-dimethylamine or polydiallyldimethylammonium chloride, alum, polyaluminum chlorides or cationic starch.
In another aspect, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish a microparticle and an effective amount of a structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
In another aspect, this invention is directed to a method of increasing retention and drainage in a papermaking furnish comprising adding to the furnish a microparticle, a coagulant and an effective amount of a structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
In another aspect, this invention is directed to a method of flocculating an aqueous coal refuse slurry comprising adding an effective amount of a structurally-modified water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.